1. Field of the Invention
The present invention related to an organic electroluminescence device, its manufacturing method and a board used therefor, and more particularly to its pattern formation.
2. Description of the Related Art
An electroluminescence (EL) device has been used as various kinds of display devices or light sources, a back light for a liquid crystal display, a light emitting device in an optical communication device, etc. The EL device is a light emitting device using electric-field light-emission of a solid fluorescent material. It is now actually used in the form of an inorganic EL device which uses an inorganic material as a light emitting material, and being developed in various applications inclusive of a back light for the liquid crystal display, flat display, etc. However, the inorganic EL device, which requires a high voltage of 100 V or more for light emission and difficult to emit blue light, has been difficult to implement its full-color display using three RGB primary colors.
On the other hand, various studies have been also made for the EL device using an organic material. However, because of its poor efficiency of light emission, it has not been put into real practice. In recent years, the EL device having a function-separating type of a laminated structure has been proposed in which the organic material is separated into a hole transporting layer and a light emitting layer. It has been verified that the organic EL can provide high luminance at a low voltage of 10 V or lower. Since then, the organic EL device has drawn great attention. Also now, the organic EL device having a function-separating type of separation structure is being studied widely.
An explanation will be given of the structure and operation of an ordinary EL device. The EL device has a laminated structure composed of a first electrode formed on the surface of a transparent glass substrate by sputtering or resistive-heating evaporation technique, a light emitting layer formed thereon and a second electrode formed thereon by a vacuum evaporation technique. The first electrode is made of a transparent conductive material such as indium tin oxide (ITO). The light emitting layer is made of poly (2-methoxy-5-dodecyloxy-p-phenylene vinylene) (hereinafter referred to as MDOPPV). The second electrode is made of metal such as Aluminum (Al).
In operation, when a DC voltage is applied to the EL device having such a structure, holes are injected from the first electrode into the light emitting layer, and electrons are injected from the second electrode into the light emitting layer. The recombination of holes and electrons occurs in the light emitting layer. When the exitons thus created decay from an excited state to a ground state, the phenomenon of light emission occurs. A various light emission color can be obtained by changing the molecular structure of an organic compound.
Meanwhile, it is known that the property of the polymer such as MDOPPV used for this light emitting layer varies drastically by photo-oxidation. Specifically, bleaching of optical absorption is observed, which is whitening corresponding to the inter-band transition which is attributable to shortening of the effective xcfx80 conjugated length and reduction of the molecular weight. In this way, extinction of photoluminescence by the photo-irradiation in the air has been studied. The light extinction is due to the defect such as a carbonyl group which operates as a light extinction center for light emission species such as exitons or exitons-polarons.
A technique of patterning the EL device using such a phenomenon has been proposed. This technique, however, performs the photo-irradiation for patterning the light-emitting layer in an atmosphere of oxygen prior to forming a second electrode. In this technique, since the second electrode must be formed after the pattern has been formed, when the substrate is heated at a high temperature in a vacuum evaporation step, the device region deteriorates greatly and the light emitting region does not emit light favorably, thus making it impossible to give sufficient contrast.
Further, there is a phenomenon that the center of light extinction is widened so that the non-light-emitting region is extended and the contour of an image is also extended.
Further, since the patterning is completed through the vacuum evaporation step starting from photo-irradiation for forming an image, it takes a long time from determination of an image to be formed to its completion. Namely, the TAT (turn around time) is disadvantageously long. Under such a circumstance, the present invention has been accomplished.
A first object of the present invention is to provide a reliable organic electroluminescence (EL) device which can provide high contrast.
A second object of the present invention is to provide a method for manufacturing an organic EL device in a short time from its order to completion and with good workability.
A third object of the present invention is to provide a reliable board for a display device which can provide high contrast.
In order to attain the first object, in accordance with a first aspect of the present invention, there is provided an organic electroluminescence device comprising: a substrate; a first electrode formed on the substrate; a light emitting layer formed on the first electrode; and a second electrode formed on the light emitting layer and made of an oxygen-transmittable material, wherein the light-emitting layer includes an oxide layer selectively formed by the selective photo-oxidation using light and oxygen reached through the second electrode, and the oxide layer constitutes (serves as) a non-light-emitting region.
In this configuration, after the second electrode is formed, light-emitting species in a local region in the light emitting layer are extinguished by selective photo-oxidation using oxygen reached through the second electrode. Therefore, a vacuum evaporation step for forming the second electrode is not required after a pattern is formed. Thus, the substrate is not heated to a high temperature and hence a device region is not deteriorated, thereby providing sufficient contrast. In addition, since the vacuum evaporation step is not carried out, a phenomenon owing to the temperature in this step, i.e. that the center of light extinction is extended, the non-light-emitting region is expanded and the contour of an image is expanded, does not occur. Further, since the patterning is completed starting from photo-irradiation for creating an image and through the vacuum evaporation, it can be implemented in a short time from determination of the image to be formed to its completion. The oxide layer may not be formed over the entire depth of the light emitting layer, but may be partially formed therein.
A second aspect of the device is an organic electroluminescence device according to the first aspect wherein the substrate is made of a light-transmittable material and the first electrode is also made of a light transmittable material; and the non-light-emitting region is formed through invasion of oxygen from the side of the second electrode and photo-oxidation based on photo-irradiation from the side of the substrate.
In this configuration, since oxygen is supplied to the light emitting layer from the side of the second electrode and photo-irradiation is done from the side of the substrate, after the pattern is formed, the second electrode is covered with a protective layer so that it is protected from transmittance of oxygen. This permits the life of the electroluminescence device to be lengthened.
A third aspect of the device is an organic electroluminescence device according to the firs aspect, wherein the second electrode is made of a light-transmittable material and the non-light-emitting region is formed by photo-oxidation using light transmitted through the second electrode.
In this configuration, since the second electrode is made of a light-transmittable material and photo-irradiation is done from the side of the second electrode, a mask can be located more closely to the second electrode, thereby improving the pattern accuracy.
A fourth aspect of the device is an organic electroluminescence device according to the first aspect, wherein the second electrode is made of a light-transmittable material, and the non-light-emitting region is formed by photo-oxidation using light transmitted through the second electrode and light from the substrate side.
In this configuration, since patterning can be done through the photo-irradiation from both sides, an image with a clear pattern or clear contour can be obtained with great accuracy.
A fifth aspect of the device is an organic electroluminescence device according to the first aspect, wherein, the second electrode is made of aluminum. The second electrode, which is semi-transparent and permits oxygen to transmit, is more effectively used.
A sixth aspect of the device is an organic electroluminescence device according to the fifth aspect, wherein the second electrode has light transmittance of 30% or higher to visible light. The second electrode is semi-transparent and transmits oxygen so that it can supply a sufficient amount of oxygen and light. Such a second electrode can be more effectively used.
A seventh aspect of the device is an organic electroluminescence device according to the fifth aspect, wherein the second electrode is made of a light-tight conductive film having an opening diameter enough to transmit oxygen molecules. The second electrode can supply a sufficient amount of oxygen and hence can be more effectively used.
A eighth aspect of the device is an organic electroluminescence device, wherein the device comprises: a substrate; a first electrode formed on the substrate; a light emitting layer formed on the first electrode; and a second electrode formed on the light emitting layer; and an oxygen supplying layer which is formed within the light-emitting layer or in the vicinity of the light-emitting layer and can supply oxygen to the light-emitting layer, wherein the light-emitting layer includes an oxide layer selectively formed by the selective photo-oxidation using light and oxygen reached through the second electrode, and the oxidized layer serves as a non-light-emitting region.
In this configuration, since the oxygen supplying layer is provided separately, the selective photo-oxidation can be made without supplying oxygen from the exterior and supply in/out of oxygen is not done, thereby lengthening the life of the organic electroluminescence device.
In order to attain the second object, a ninth aspect of the method is a method of manufacturing an organic electroluminescence device comprising the steps of: forming a first electrode formed on the surface of a substrate; forming a light emitting layer formed on the first electrode; forming a second electrode formed on the light emitting layer to form a sandwiching structure in which the light-emitting layer is sandwiched between the first electrode and the second electrode; and exposing a pattern by selectively irradiating the sandwiching structure with light from the side of the first electrode or second electrode to form a non-light-emitting region of an oxide region through selective photo-oxidation.
A tenth aspect of the method is method of manufacturing an organic electroluminescence device according to the ninth aspect, wherein, the second electrode is made of a light-transmittable porous thin film enough to transmit oxygen and light., and the step of making pattern light-exposure is carried out through photo-oxidation by photo-irradiation from side of the second electrode.
An eleventh aspect of the method is a method of manufacturing an organic electroluminescence device according to the ninth aspect, wherein the second electrode is made of a light transmittable porous thin film having light-transparency enough to transmit oxygen, and the step of making pattern light-exposure is carried out through photo-oxidation by photo-irradiation from the side of the first electrode.
An twelfth aspect of the method is a method of manufacturing an organic electroluminescence device according to the ninth aspect, wherein the first or second electrode, or the light emitting layer includes an oxygen supplying layer which can supply oxygen, and the step of making pattern light-exposure is carried out through photo-oxidation by supply of the oxygen from the oxygen supplying layer.
In order to attain the third object, a thirteenth aspect of the board is a board for a display device of the present invention, comprising: a substrate; a first electrode formed on the substrate; a light emitting layer formed on the first electrode; and a second electrode formed on the light emitting layer, wherein the second electrode is made of a porous thin film enough to transmit oxygen, and the light-emitting layer is designed to provide an oxide layer selectively formed by the selective photo-oxidation using photo-irradiation and oxygen reached through the second electrode, the oxide layer serves as a non-light-emitting region.
A fourteenth aspect of the board is a board for a display device according to the thirteenth aspect, wherein the second electrode is made of a light-transmittable porous thin film enough to transmit oxygen and light, wherein the light-emitting layer:. is designed to provide an oxide layer selectively formed by the selective photo-oxidation using photo-irradiation from the side of the second electrode and oxygen reached through the second electrode, the oxide layer serving as a non-light-emitting region.
A fifteenth aspect of the board is a board for a display device according to the thirteenth aspect, wherein the second electrode is made of a light-tight porous thin film enough to transmit oxygen, the substrate is made of a light-transmittable material, the first electrode is made of a light-transmittable material and the light-emitting layer is designed to provide an oxide layer selectively formed by the selective photo-oxidation using photo-irradiation from the side of the first electrode and oxygen reached through the second electrode, the oxide layer serving as a non-light-emitting region.
A sixteenth aspect of the board is a board for a display device of the present invention which comprises: a substrate; a first electrode formed on the substrate; a light emitting layer formed on the first electrode; a second electrode formed on the light emitting layer; and an oxygen supplying layer which is formed within the light-emitting layer or in the vicinity of the light-emitting layer and can supply oxygen to the light-emitting layer, wherein the light-emitting layer is designed to provide an oxide layer selectively formed by the selective photo-oxidation using photo-irradiation and oxygen reached through the second electrode, the oxide layer serving as a non-light-emitting region.
A seventeen aspect of the board is a board for a display device according to the sixteenth aspect, wherein the second electrode is made of aluminum.
An eighteenth aspect of the board is a board for a display device according to the sixteenth aspect, wherein the second electrode has light transmittance of 30% or higher to visible light.
In accordance with the present invention, after the second electrode is formed, light-emitting species of a local region in the light emitting layer are extinguished by selective photo-oxidation using oxygen reached through the second electrode so that the non-light-emitting region is formed so as to surround a light emitting pattern. Therefore, a vacuum evaporation step for forming the second electrode is not required after the pattern is formed, thereby providing an electroluminescence device with high contrast and with great reliability. The patterning can be carried out very easily and with improve workability.
The basic idea of the present invention is as follows.
(i) The light emitting species created electrically in conductive polymer (emission layer) are extinguished by quenching centor such as the carbonyl group created by photo-oxidation.
(ii) The electric conductivity of the conductive polymer (emission layer) can be reduced by shortening of the effective conjugated length by the photo-oxidation.
(iii) The charge injecting efficiency at an electrode/polymer interface is reduced by the photo-oxidation of the polymer at the interface.
In this structure described above, an image can be printed very easily on the organic electroluminescence device. Therefore, a consumer who purchased a greeting card can print a desired pattern thereon on the basis of the principle similar to a (sunshine) photograph. It can be also applied to a name plate which can be sold at a place such a holiday carpenter center after the desired name is immediately printed. Further, it can be applied to a number plate of a motor car. In this case, the time from its order to delivery can be shortened greatly.
Accordingly, the organic electroluminescence device and board for a display device with high light-emitting efficiency and high contrast can be obtained.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.